Hey Wayne (or who every else might know the answer),
I used the Arcing ball bounce start file labeled 2.8 and was following along with the exercise video except when it came to the function line for the x-axis mine was increasing on x & y rather than decreasing on x & y like in Wayne's video. It seemed to look OK anyway but I don't understand why my y increased rather than decreased. I am using Blender 2.91.2.
Ciao